Chemically amplified positive photoresists

ABSTRACT

Photoresist compositions are provided comprising 1) a resin binder having photoacid-labile groups, 2) an acid generator and 3) a photospeed control agent. Photoresists of the invention exhibit good photospeed and can provide highly resolved relief images of small dimensions, including lines of sub-micron and sub-half micron dimensions with at least essentially vertical side walls. Methods are also provided that include control of photospeed of a photoresist composition of the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to new photoresist compositions particularlysuitable for deep U.V. exposure and having the capability of forminghighly resolved features submicron dimension.

2. Background

Photoresists are photosensitive films for transfer of images to asubstrate. They form negative or positive images. After coating aphotoresist on a substrate, the coating is exposed through a patternedphotomask to a source of activating energy such as ultraviolet light toform a latent image in the photoresist coating. The photomask has areasopaque and transparent to activating radiation that define a desiredimage to be transferred to the underlying substrate. A relief image isprovided by development of the latent image pattern in the resistcoating. The use of photoresists is generally described, for example, byDeforest, Photoresist Materials and Processes, McGraw Hill Book Company,New York (1975), and by Moreau, Semiconductor Lithography, Principals,Practices and Materials, Plenum Press, New York (1988).

More recently, certain "chemically amplified" photoresist compositionshave been reported. Such photoresists may be negative-acting orpositive-acting and rely on many crosslinking events (in the case of anegative-acting resist) or deprotection reactions (in the case of apositive-acting resist) per unit of photogenerated acid. In other words,the photogenerated acid acts catalytically. In the case of the positivechemically amplified resists, certain cationic photoinitiators have beenused to induce cleavage of certain "blocking" groups pendant from aphotoresist binder, or cleavage of certain groups that comprise aphotoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199;4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian PatentApplication 2,001,384. Upon selective cleavage of the blocking groupthrough exposure of a coating layer of such a resist, a polar functionalgroup is provided, e.g., carboxyl or imide, which results in differentsolubility characteristics in exposed and unexposed areas of the resistcoating layer.

An important property of a photoresist is image resolution. A developedphotoresist image of fine line definition, including lines of sub-micronand sub-half micron dimensions and having vertical or essentiallyvertical sidewalls is highly desirable to permit accurate transfer ofcircuit patterns to an underlying substrate. However, many currentphotoresists are not capable of providing such highly resolved fine lineimages.

Another important property of a photoresist is photospeed, which can bedefined as the exposure time coupled with the exposure energy requiredto activate the photoactive component, e.g. to generate the requiredamount of photoacid to provide the desired solubility differentialbetween exposed and unexposed areas of a photoresist coating layer.

It can be critical that a resist's photospeed is within an acceptableand consistent range or value to permit desired processing of theresist. For instance, sufficiently high photospeed is important in manyprocesses, e.g. where a number of exposures are needed such as ingenerating multiple patterns by a step and repeat process, or whereactivating energy of reduced intensity is employed. Sufficiently highphotospeed also permits reduction in the concentration of the radiationsensitive component in the photoresist. On the other hand, a resist thatis "too fast", i.e. has too high photospeed, can be undesirable. Forexample, an extremely high photospeed may compromise resolution of thepatterned resist image and/or exposure equipment may not be well suitedto image fast resists.

Moreover, a consistent photospeed of a resist can be critical, e.g. sothat a device manufacturer can use the same imaging conditions andobtain consistent results despite lot-to-lot differences of a resistproduct (such as precise amount and/or nature of photoactive compound,resin, etc.) that may frequently occur, particularly in large scaleresist manufacturing processes. However, many current resists do notexhibit such consistent photospeed, and consequently a devicemanufacturer may either realize inconsistent results as different lotsof a resist formulation are used, or the device manufacturer may beforced to carefully test the photospeed of each new lot of resist andthen adjust the parameters of the exposure equipment to provide forconsistent processing. Clearly, either alternative is undesirable.

Relatively recently interest has increased in photoresists that can bephotoimaged with deep U.V. radiation. Such photoresists offer thepotential of forming images of smaller features than may be possible atlonger wavelength exposure. As is recognized by those in the art, "deepU.V. radiation" refers to exposure radiation having a wavelength in therange of about 350 nm or less, more typically in the range of about 300nm or less. While a number of deep U.V. resists have been reported, theneed clearly exists for new deep U.V. resists that can provide highlyresolved fine line images as well as acceptable photospeed and otherlithographic properties.

It thus would be desirable to have new chemically amplified photoresistcompositions that could provide highly resolved fine line images,including images of sub-micron and sub-half micron dimensions. It wouldbe further desirable to have such new photoresist compositions thatcould be imaged with deep U.V. radiation. It would be particularlydesirable to have such a chemically amplified photoresist where theresist's photospeed was capable of being carefully controlled to aspecific value or narrow range of values.

SUMMARY OF THE INVENTION

The present invention provides new photoresist compositions that ingeneral comprise 1) a resin binder having photoacid labile groups, 2) anacid generator and 3) a photospeed control agent.

It has been found that photoresists of the invention can provide highlyresolved relief images of small dimensions, including lines ofsub-micron and sub-half micron dimensions with vertical or essentiallyvertical side walls.

It also has been surprisingly found that the photospeed control agentimparts an acceptable photospeed to resists of the invention.

Moreover, the photospeed control agent enables providing a consistentphotospeed of the resist. That is, the photospeed of a particular resistcomposition of the invention can be precisely fixed at a specified valueby use of the photospeed control agent. This is a significant advantageas photospeed differences between production lots of the resist can becompensated for by use of the photospeed control agent to provideuniform photospeed. In this regard, the invention includes methods forproviding a consistent photospeed of the resist compositions of theinvention, which comprise adjusting the photospeed of a resistcomposition to a desired value by altering the concentration of thephotospeed control agent in the composition.

The photospeed control agent is preferably a strong base, particularlyan organic amine, and more preferably is an organic salt of a strongbase. Ammonium and phosphonium are particularly preferred bases to usein salt form. Especially preferred are salts of a compound substitutedby hydroxy and carbonyl such as a lactate salt as well as sulfonyl saltssuch as a triflate or tosylate. It has been found that a photospeedcontrol agent counter ion that is a hydroxy-substituted alkanoylprovides better performance results than a comparable composition thatincludes a counter ion of a photospeed control agent that is an alkanoylwithout hydroxy substitution.

Phenolic resins are generally preferred resin binders of resists of theinvention. Particularly preferred are copolymers of vinyl phenol andother copolymerizable group(s), especially where the acid labile groupsare present substantially, essentially or completely only onnon-phenolic units of the copolymer. Preferred copolymer binders includecopolymers that comprise substituted or unsubstituted phenol(s) and oneor more alkylacrylates such as t-butylacrylate or t-butylmethacrylate.Non-phenolic resin binders are also suitable, e.g. copolymers of one ormore alkyl acrylates and vinyl alicylics. Preferred acid labile groupsare pendant from the resin binder backbone.

Another preferred component of resist compositions of the invention is adye compound. Preferred dyes will enhance resolution of the patternedresist image, typically by reducing reflections and the effects thereof(e.g. notching) of the exposure radiation, while permitting efficientimaging. Preferred dyes of compositions of the invention includesubstituted and unsubstituted phenothiazine, phenoxazine, anthracene andanthrarobin compounds as well as copolymers thereof such as ananthracene acrylate copolymer.

The invention also provided methods for forming relief images of thephotoresist compositions of the invention, including methods for forminghighly resolved patterned photoresist images (e.g., a patterned linehaving essentially vertical sidewalls) of sub-micron or sub-half microndimensions. The invention further provides articles of manufacturecomprising substrates such as a microelectronic wafer or a flat paneldisplay substrate having coated thereon the photoresists and reliefimages of the invention.

Other aspects of the invention are disclosed infra.

DETAILED DESCRIPTION OF THE INVENTION

The resin binder component of the photoresists of the invention suitablycontains phenol units and has acid labile groups, typically pendant fromthe resin backbone, and typically used in a resist composition of theinvention in an amount sufficient to render an exposed coating layer ofthe resist developable such as with an aqueous alkaline solution.Exemplary phenolic resins containing such acid labile groups aredisclosed in the above mentioned patents such as U.S. Pat. No. 4,491,628to Ito as well as in U.S. Pat. No. 5,258,257 to Sinta et al. Such resinscan be prepared by alkaline condensation of the preformed phenolic resinwith a compound that comprises the acid labile group and a suitableleaving group. For example, to provide acetate acid labile groupspendant to the resin binder backbone, the preformed resin binder may becondensed with a compound of the formula L--CR¹ R² C(═O)--O--R³, where Lis a leaving group such as bromide or chloride, R¹ and R² are eachindependently hydrogen, an electron withdrawing group such as halogen(particularly F, Cl or Br), or substituted or unsubstituted C₁₋₁₀ alkyl;and R³ is substituted or unsubstituted C₁₋₁₀ alkyl, or substituted orunsubstituted aryl such as phenyl or aryalkyl such as benzyl. Thecondensation provides the groups of the formula --CR¹ R² C(═O)--O--R³pendant to the resin binder backbone and grafted onto the resin'savailable hydroxyl groups. Photoacid degradation of those groups duringexposure and/or post-exposure heating provides the polar acetic acidether moiety pendant to the resin binder backbone. Other acid labilegroups of course also may be employed, e.g. oxycarbonyl groups such asthose of the formula --C(═O)OR³ where R³ is as defined above andpreferably is t-butyl or benzyl. See also U.S. Pat. No. 5,258,257 toSinta et al. for a discussion of acid labile groups and preparation anduse of resist resin binders comprising acid labile groups.

It is generally preferred that the resin binder is a copolymer of vinylphenol and other copolymerizable group(s). Preferred copolymers compriseunits of substituted or unsubstituted phenols and non-aromatic groups,particularly copolymers of vinyl phenols and alkyl acrylates, typicallyC₁₋₁₂ alkyl acrylates. Particularly preferred are copolymers of vinylphenols and acrylates having branched alkyl chains, such as copolymersformed from t-butyl acrylate, t-butyl methacrylate, etc.

As mentioned above, it is preferred to have acid labile groupssubstantially or completely only on non-phenolic or other non-aromaticunits of the copolymer binder. One especially preferred copolymer binderhas repeating units x and y of the following formula: ##STR1## whereinthe hydroxyl group be present at either the ortho, meta or parapositions throughout the copolymer, and R is substituted orunsubstituted alkyl having 1 to about 18 carbon atoms, more typically 1to about 6 to 8 carbon atoms. Tert-butyl is a generally preferred Rgroup. An R group may be optionally substituted by e.g. one or morehalogen (particularly F, Cl or Br), C₁₋₈ alkoxy, C₂₋₈ alkenyl, etc. Theunits x and y may be regularly alternating in the copolymer, or may berandomly interspersed through the polymer.

Such copolymers can be readily formed. For example, for resins of theabove formula, vinyl phenols and a substituted or unsubstituted alkylacrylate such as t-butylacrylate and the like may be condensed underfree radical conditions as known in the art. The substituted estermoiety, i.e. R--O--C(═O)--, moiety of the acrylate units serves as theacid labile groups of the resin and will undergo photoacid inducedcleavage upon exposure of a coating layer of a photoresist containingthe resin. Preferably the copolymer will have a M_(W) of from about8,000 to about 50,000, more preferably about 15,000 to about 30,000 witha molecular weight distribution of about 3 or less, more preferably amolecular weight distribution of about 2 or less. Non-phenolic resins,e.g. a copolymer of an alkyl acrylate such as t-butylacrylate ort-butylmethacrylate and a vinyl alicyclic such as a vinyl norbornanyl orvinyl cyclohexanol compound, also may be prepared by such free radicalpolymerization or other known procedures and suitably will have a M_(W)of from about 8,000 to about 50,000, and a molecular weight distributionof about 3 or less.

The photoresist compositions of the invention also comprise a photospeedcontrol agent. The photospeed control agent is a strong base in non-saltform, particularly a base having a pK_(a) of about 10 or greater, morepreferably a pK_(a) of about 10.5 or 11 or greater. When complexed as asalt as disclosed herein, the photospeed control agent will have a lowerpK_(a), e.g. a pK_(a) of about 9 or less, more typically from about 5 to9. As used herein, the term "pK_(a) " is used in accordance with its artrecognized meaning, that is, pK_(a) is the negative log (to the base 10)of the dissociation constant of the polar compound in aqueous solutionat about room temperature.

Organic bases are generally preferred photospeed control agents,particularly organic amines such as a tetra-alkylammonium compound, e.g.tetrabutylammonium hydroxide (TBAH).

Even more preferred is to use a salt as a photospeed control agent,particularly a salt of an organic acid such as salt of lactic acid,succinic acid, citric acid, etc. A lactate salt is generally preferred,particularly a lactate salt of an organic amine such as atetrabutylammonium compound or other tetraalkylammonium agent. Sulfonylsalts are also preferred such as a triflate or tosylate. Ammonium andphosphonium are preferred bases to use in salt form. It has been foundthat resolution of resist relief images of the invention will be evenfurther enhanced by use of such a salt as a photospeed control agentrelative to a comparable composition that contains the agent in non-saltform.

One preferred group of photospeed control agents of the invention have aformula of N(R¹)₄ A, where each R¹ is independently substituted orunsubstituted alkyl preferably having from 1 to about 12 carbon atoms,more typically 1 to about 8 carbon atoms, or a substituted orunsubstituted aryl such as a C₆₋₁₀ aryl e.g. phenyl, naphthyl and thelike; and A is a counter anion of a halide, a substituted orunsubstituted hydroxyalkanoyl preferably having 1 to about 18 carbonatoms (i.e. a group substituted by hydroxy and carbonyl such aslactate--CH₃ CH(OH)C(═O)0⁻), substituted or unsubstituted sulfonateincluding a C₆₋₁₈ aryl or C₁₋₁₂ alkyl sulfonate. The termhydroxyalkanoyl as used herein refers to an alkanoyl group having one ormore hydroxy moieties (typically 1, 2, 3 or 4 hydroxy moieties) on oneor more carbons of the alkanoyl group. Exemplary sulfonate A groupsinclude mesylate, triflate, tosylate, etc. Substituted A groups may besuitably substituted by one or more groups such as halo particularlyfluoro, chloro and bromo, hydroxy, cyano, nitro, C₁₋₁₂ alkyl, C₂₋₁₂alkenyl, C₁₋₁₂ alkoxy, C₁₋₁₂ alkanoyl including acyl, etc.

As discussed above, a phosphonium compound also may be employed as aphotospeed control, including phosphonium salts such as e.g. compoundsof the formula P(R¹)₄ A where R¹ and A are each the same as definedabove for the formula N(R¹)₄ A.

Such salts of a photospeed control agent can be readily prepared byknown procedures, e.g., by dissolving the free base in an aqueoussolution containing the acid and then removing solvent or,alternatively, reacting the free base and acid in an organic solventsuch as chloroform or the like and then isolating the salt. Thephotospeed control agent in salt or non-salt form, as well as all othercomponents of a resist composition of the invention, should be solublein the resist organic solvent carrier(s) so as to provide a formulationthat is at least essentially particle-free. See also the examples whichfollow.

The resist compositions of the invention also comprise a photoacidgenerator (i.e. "PAG") that is suitably employed in an amount sufficientto generate a latent image in a coating layer of the resist uponexposure to activating radiation. Generally, sulfonate compounds arepreferred PAGs, particularly sulfonate salts. Two specifically preferredagents are of the following formulae I and II: ##STR2##

Such sulfonate compounds can be prepared in accordance with thefollowing scheme which depicts the synthesis of a compound of formula I.See also Example 2 which follows for synthesis of that PAG. The PAG offormula II can be prepared as generally depicted in the below Scheme andExample 2, except approximately molar equivalents of t-butyl benzene andbenzene would be reacted together in the first step with aceticanhydride and KIO₃. ##STR3##

Sulfonated esters including sulfonyloxy ketones are also preferred PAGsof resist compositions of the invention. Suitable sulfonated esters havebeen reporting in J. of Photopolymer Science and Technology, vol. 4, No.3,337-340 (1991), incorporated herein by reference, including benzointosylate, t-butylphenyl alpha-(p-toluenesulfonyloxy)-acetate and t-butylalpha-(p-toluenesulfonyloxy)-acetate. Preferred sulfonate PAGs are alsodisclosed in U.S. Pat. No. 5,344,742 to Sinta et al.

Onium salts are also generally preferred acid generators of compositionsof the invention. Onium salts that weakly nucleophilic anions have beenfound to be particularly suitable. Examples of such anions are thehalogen complex anions of divalent to heptavalent metals or non-metals,for example, Sb, Sn, Fe, Bi, Al, Ga, In, Ti, Zr, Sc, D, Cr, Hf, and Cuas well as B, P, and As. Examples of suitable onium salts arediaryl-diazonium salts and onium salts of group Va and B, Ia and B and Iof the Periodic Table, for example, halonium salts, quaternary ammonium,phosphonium and arsonium salts, aromatic sulfonium salts and sulfoxoniumsalts or selenium salts. Examples of suitable preferred onium salts canbe found in U.S. Pat. Nos. 4,442,197; 4,603,101; and 4,624,912.

Other useful acid generator include the family of nitrobenzyl esters,and the s-triazine derivatives. Suitable s-triazine acid generators aredisclosed, for example, in U.S. Pat. No. 4,189,323.

Non-ionic photoacid generators are suitable including halogenatednon-ionic, photoacid generating compounds such as, for example, 1,1-bisp-chlorophenyl!-2,2,2-trichloroethane (DDT); 1,1-bisp-methoxyphenyl!-2,2,2-trichloroethane;1,2,5,6,9,10-hexabromocyclodecane; 1,10-dibromodecane; 1,1-bisp-chlorophenyl!-2,2-dichloroethane;4,4-dichloro-2-(trichloromethyl)benzhydrol(Kelthane); hexachlorodimethylsulfone; 2-chloro-6-(trichloromethyl)pyridine;o,o-diethyl-o-(3,5,6-trichloro-2-pyridyl)phosphorothionate;1,2,3,4,5,6-hexachlorocyclohexane; N(1,1-bisp-chlorophenyl!-2,2,2-trichloroethyl)acetamide; tris2,3-dibromopropyl!isocyanurate; 2,2-bisp-chlorophenyl!-1,1-dichloroethylene; tris trichloromethyl!s-triazine;and their isomers, analogs, homologs, and residual compounds. Suitablephotoacid generators are also disclosed in European Patent ApplicationNos. 0164248 and 0232972.

Acid generators that are particularly preferred for deep U.V. exposureinclude 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT);1,1-bis(p-methoxyphenol)-2,2,2-trichloroethane;1,1-bis(chlorophenyl)-2,2,2 trichloroethanol;tris(1,2,3-methanesulfonyl)benzene; and tris(trichloromethyl)triazine.

Another preferred component of resist compositions of the invention is adye compound. Preferred dyes will enhance resolution of the patternedresist image, typically by reducing reflections and the effects thereof(e.g. notching) of the exposure radiation. Preferred dyes includesubstituted and unsubstituted phenothiazine, phenoxazine, anthracene andanthrarobin compounds. Preferred substituents of substitutedphenothiazine, phenoxazine, anthracene and anthrarobin include e.g.halogen, C₁₋₁₂ alkyl, C₁₋₁₂ alkoxy, C₂₋₁₂ alkenyl, C₁₋₁₂ alkanoyl suchas acetyl, a as phenyl, etc. Copolymers of such compounds also may beused as a dye, e.g., an anthracene acrylate polymer or copolymer. Seefor instance Example 5 which follows. A curcumin dye also may be usedfor some applications. In addition to reducing reflections in deep U.V.exposures, use of a dye may expand the spectral response of thecompositions of invention.

Photoresists of the invention also may contain other optional materials.For example, other optional additives include anti-striation agents,plasticizers, speed enhancers, etc. Such optional additives typicallywill be present in minor concentration in a photoresist compositionexcept for fillers and dyes which may be present in relatively largeconcentrations such as, e.g., in amounts of from about 5 to 30 percentby weight of the total weight of a resist's dry components.

The compositions of the invention can be readily prepared by thoseskilled in the art. For example, a photoresist composition of theinvention can be prepared by dissolving the components of thephotoresist in a suitable solvent such as, for example, a glycol ethersuch as 2-methoxyethyl ether (diglyme), ethylene glycol monomethylether, ethylene glycol monomethyl ether, propylene glycol monomethylether; a Cellosolve ester such as methyl ethyl ketone. Typically, thesolids content of the composition varies between about 5 and 35 percentby weight of the total weight of the photoresist composition. The resinbinder and PAG components should be present in amounts sufficient toprovide a film coating layer and formation of good quality latent andrelief images. See the examples which follow for exemplary preferredamounts of resist components. The photospeed control agent can beemployed in relatively small amounts, e.g. about 1% to 20% by weightrelative to the PAG.

The compositions of the invention are used in accordance with generallyknown procedures. The liquid coating compositions of the invention areapplied to a substrate such as by spinning, dipping, roller coating orother conventional coating technique. When spin coating, the solidscontent of the coating solution can be adjusted to provide a desiredfilm thickness based upon the specific spinning equipment utilized, theviscosity of the solution, the speed of the spinner and the amount oftime allowed for spinning.

In accordance with the invention, after formulation of the resist, asample of the resist can be tested for its photospeed and the photospeedadjusted, if needed, to provide a photospeed of a desired value byaltering the concentration of the photospeed control agent in the resistformulation. For example, if the resist photospeed is too high, anadditional amount of the control agent can be added to the formulation,and a further sample tested to ensure the resist then exhibits thedesired photospeed. The photospeed of a resist of the invention can bedetermined by procedures well known to those in the art, such as theprocedure disclosed in U.S. Pat. No. 4,618,233 to Hertlein. A resistcomposition of the invention preferably will contain a sufficientconcentration of the photospeed control agent so that only a 3 percentor less, or more preferably about 1 to 2 percent or less, difference inphotospeed exists between lots or batches.

The resist compositions of the invention are suitably applied tosubstrates conventionally used in processes involving coating withphotoresists. For example, the composition may be applied over siliconor silicon dioxide wafers for the production of microprocessors andother integrated circuit components. Aluminum-aluminum oxide, galliumarsenide, ceramic, quartz or copper substrates also may be employed.Substrates used for liquid crystal display and other flat panel displayapplications are also suitably employed, e.g. glass substrates, indiumtin oxide coated substrates and the like.

Following coating of the photoresist onto a surface, it is dried byheating to remove the solvent until preferably the photoresist coatingis tack free. Thereafter, it is imaged through a mask in conventionalmanner. The exposure is sufficient to effectively activate thephotoactive component of the photoresist system to produce a patternedimage in the resist coating layer and, more specifically, the exposureenergy typically ranges from about 10 to 300 mJ/cm², dependent upon theexposure tool and the components of the photoresist composition.

Coating layers of the resist compositions of the invention arepreferably photoactivated by an exposure wavelength in the deep U.V.range i.e., 350 nm or less, more typically in the range of about 300 nmor less, typically about 150 to 300 or 350 nm. A particularly preferredexposure wavelength is about 248 nm.

Following exposure, the film layer of the composition is preferablybaked at temperatures ranging from about 70° C. to about 160° C.Thereafter, the film is developed. The exposed resist film is renderedpositive working by employing a polar developer, preferably an aqueousbased developer such as an inorganic alkali exemplified by sodiumhydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate,sodium silicate, sodium metasilicate; quaternary ammonium hydroxidesolutions such as a tetra-alkyl ammonium hydroxide solution; variousamine solutions such as ethyl amine, n-propyl amine, diethyl amine,di-n-propyl amine, triethyl amine, or methyldiethyl amine; alcoholamines such as diethanol amine or triethanol amine; cyclic amines suchas pyrrole, pyridine, etc. In general, development is in accordance withart recognized procedures.

Following development of the photoresist coating over the substrate, thedeveloped substrate may be selectively processed on those areas bared ofresist, for example by chemically etching or plating substrate areasbared of resist in accordance with procedures known in the art. For themanufacture of microelectronic substrates, e.g., the manufacture ofsilicon dioxide wafers, suitable etchants include a plasma gas etch(e.g. an oxygen plasma etch) and a hydrofluoric acid etching solution.The compositions of the invention are highly resistant to such etchantsthereby enabling manufacture of highly resolved features, includinglines with submicron widths. After such processing, resist may beremoved from the processed substrate using known stripping procedures.

All documents mentioned herein are incorporated herein in their entiretyby reference.

The following non-limiting examples are illustrative of the invention.

EXAMPLE 1

Preparation of photospeed control agent of tetra-n-butylammoniumd/l-lactate salt (CH₃ CH₂ CH₂ CH₂)₄ NO(CO)CH(OH)CH₃ !

To a solution of tetra-n-butylammonium bromide (16.12 g, 50.0 mmol) inwater (50 ml) was added a gray colored suspension of silver lactate(9.85 g, 50.0 mmol) in water (100 ml). As the addition proceeded agrayish white solid, presumably silver bromide, precipitated fromsolution. The resulting suspension was stirred at room temperature for15 hours, the solid was filtered off and washed with water (3×50 ml).The combined filtrate and washings were concentrated under reducedpressure and the residual oil dried in vacuo at 50° C. for 24 hours togive the title compound as a colorless oil (16.62 g, 99%). Upon standingat room temperature, this oil later formed a waxy semi-solid.

EXAMPLE 2

Preparation of di-(4-t-butylphenyl)iodonium (±)-10-camphor sulfonate(compound of formula I above)

A 2 L 3 neck round bottom flask was charged with potassium iodate(214.00 g, 1.00 mol), t-butylbenzene (268.44 g, 2.00 mol) and aceticanhydride (408.36 g, 4.00 mol). The flask was fitted with an efficientoverhead paddle stirrer, a thermometer and a pressure equalizingdropping funnel fitted with a N₂ bubbler. The reaction mixture wascooled to 10° C. in a ice-water bath and concentrated sulfuric acid(215.78 g, 2.20 mol) added dropwise via the addition funnel. Theaddition was carried out at such a rate as to maintain the reactiontemperature around 25° C. and required 2 hours. As the additionproceeded the starting white suspension became orange-yellow in color.Once the addition was over, the reaction mixture was stirred at roomtemperature (20° C.) for a further 22 hours. The reaction mixture wascooled to 5°-10° C. and water (600 ml) was added dropwise over @30minutes, maintaining the temperature below 30° C. (Note the first @75 mlshould be added at a particular slow rate as to control the initialexotherm, thereafter the rest of the water may be added at a fasterrate). This cloudy mixture was washed with hexane (3×100 ml) (to removeunreacted t-butylbenzene and some 4-t-butyliodobenzene byproduct) in a 2L separating funnel and the aqueous solution of diaryliodoniumhydrogensulfate transferred to a 3 L reaction vessel. The solution iscooled to 5°-10° C., (±)-10-camphorsulfonic acid (232.30 g, 1.00 mol)was added in one portion with stirring and the solution was thenneutralized with ammonium hydroxide (620 ml, 9.20 mol). The amount ofbase used was the theoretical amount required to neutralize all acidicspecies in the pot, assuming quantitative reaction. The addition of thebase is carried out at such a rate as to keep the temperature below 25°C. and takes about 1 hour. As the addition nears completion and the pHof the reaction mixture approaches 7, the crude diaryliodoniumcamphorsulfonate precipitated as a tan solid. This suspension wasallowed to stir at room temperature for 3 hours and the materialisolated as follows: The tan solid was collected by suction filtrationand while still moist taken up in dichloromethane (IL) and washed withdilute ammonium hydroxide (2.5 wt %, 5 ml 14.8N NH₄ OH+195 ml H₂ O)until the washings are in the pH 7-8 range (1×200 ml) and then water(2×200 ml) to restore the pH to around 7. After drying (MgSO₄), thedichloromethane was removed under reduced pressure and the residuefurther dried in vacuo at 50° C. for 16 hours to give the crude productas a tan solid (390.56 g). The resulting tan solid was then purified byrecrystallization in the following manner. The tan solid was dissolvedin the minimum amount of refluxing isopropanol @375 g PAG in @1150 mlIPA) in a 2 L RBF to give a homogeneous dark red solution. The hotsolution was transferred to a 2 L conical flask and allowed to cool.While this solution is still warm, hexane (500 ml) was added andcrystals form soon after. The crystallizing mixture was allowed to coolto room temperature and stored for 4 hours. The crystallizing solutionwas cooled to @5° C. in an ice-water bath for 1.5 hours and then thesolid is collected by suction filtration and washed until white withvery cold isopropanol-hexane (1:3, 2×200 ml, prepared by cooling thesolvent mixture in a dry ice-acetone bath before use). The white solidwas dried under aspirator vacuum for 1 hour until the PAG (titlecompound; photoactive active compound of formula I was isolated as afree flowing white powder. At this stage about 285 g of PAG is obtained.A second recrystallization can be performed in a similar manner.

EXAMPLES 3-4

In the following Example 3, a photoresist composition of the inventionwas prepared that contained as a lactate salt of TBAH, prepared asdescribed in Example 1 above. In Example 4, a comparable resist wasprepared which did not contain TBAH lactate or any other photospeedcontrol agent. As can be seen by comparison of the results of Examples 3and 4, use of a photospeed control agent can increase substantiallyresolution of a patterned resist image. In each of Examples 3 and 4, theresin binder was a copolymer of vinyl phenol and t-butylacrylate, havinga M_(W) of about 20,000 and available under the tradename of MaruzenCTBA 161 from Maruzen Oil Company of Tokyo, Japan. The leveling agentused in each of the examples is the commercially available material soldunder the name Silwet™ L-7604 by Union Carbide. The photoacid generator(PAG) used in the examples below is the sulfonate salt of Example 2 andformula I above. Ethyl lactate was the solvent used in each of theExamples 3-4.

Example 3

A resist formulation was prepared by admixing the following componentsin the following amounts:

    ______________________________________    Components     Amount (expressed in grams)    ______________________________________    Resin binder   4.369    PAG            0.131    Photospeed control agent                   0.013    Leveling agent 0.023    Solvent        30.311    ______________________________________

This resist formulation was spin coated onto hexamethyldimethylsilanetreated silicon wafers at 3000 rpm for 30 seconds. After soft-baking for60 seconds at 150° C. on a vacuum hot plate a tack-free resist film wasobtained. The resist film was then exposed to deep U.V. exposurewavelength using a GCA Excimer laser and stepper NA 0.35 (Eo=5.32 mj/cm²; Es=13.3 mj/cm² with Es/Eo=2.5). After exposure the resist film wasbaked at 150° C. for 90 seconds followed by immersion development in0.26N aqueous tetramethylammonium hydroxide solution for 60 seconds. Arelief image was obtained resolved to a dimension of 0.32 microns withsquare (vertical sidewalls) profile.

Example 4

A resist formulation was prepared by admixing the following componentsin the following amounts:

    ______________________________________    Components   Amount (expressed in grams)    ______________________________________    Resin binder 9.500    PAG          0.285    Leveling agent                 0.049    Solvent      41.897    ______________________________________

This resist formulation coated onto silicon wafers as described inExample 3 above. After soft-baking for 60 seconds at 150° C. on a vacuumhot plate a tack-free resist film was obtained. The resist film was thenexposed to deep U.V. exposure wavelength using a GCA Excimer laser andstepper NA 0.35 (Eo=0.59 mj/cm² ; Es=0.71 mj/cm² with Es/Eo=1.2). Afterexposure the resist film was baked at 150° C. for 90 seconds followed byimmersion development in 0.26N aqueous tetramethylammonium hydroxidesolution for 60 seconds. A relief image was obtained to a dimension of0.40 microns with undercutting and ragged profiles.

EXAMPLE 5

Photoresists containing a dye

Four different photoresists (resists A-D below) were prepared byadmixing the specified components. The resin binder for each of theresists was a copolymer of vinyl phenol and t-butylacrylate, having aM_(W) of about 20,000 and available under the tradename of MaruzenKE-610 from Maruzen Oil Company of Tokyo, Japan. Other resistcomposition components, including the dye compound, are indicated below.

Photoresist A

15.209% polymer KE-610 (38% t-butyl acrylate/62% hydroxystyrenecopolymer), 0.456% photo acid generator (di t-butylphenyl iodoniumcamphor sulfonate formula I above); 0.30% photospeed control agent(tetrabutyl ammonium hydroxide), 0.080% leveling agent (Silwet™ L-7604),0.304% dye (9-anthracenemethyl methacrylate/2-hydroxyethyl methacrylatecopolymer, 50/50 w/w) and 83.920% ethyl lactate.

Photoresist B

15.209% polymer KE-610 (38% t-butyl acrylate/62% hydroxystyrenecopolymer), 0.456% photo acid generator (di t-butylphenyl iodoniumcamphor sulfonate (formula I above); 0.30% photospeed control agent(tetrabutyl ammonium hydroxide), 0.080% leveling agent (Silwet™ L-7604),0.304% dye (2-acetylphenothiazine) and 83.920% ethyl lactate.

Photoresist C

15.209% polymer KE-610 (38% t-butyl acrylate/62% hydroxystyrenecopolymer), 0.456% photo acid generator (di t-butylphenyl iodoniumcamphor sulfonate formula I above; 0.30% photospeed control agent(tetrabutyl ammonium hydroxide), 0.080% leveling agent (Silwet™ L-7604),0.304% dye (Anthrarobin) and 83.920% ethyl lactate.

Photoresist D

14.787% polymer KE-610 (38% t-butyl acrylate/62% hydroxystyrenecopolymer), 0.444% photo acid generator (di t-butylphenyl iodoniumcamphor sulfonate formula I above), 0.30% photospeed control agent(tetrabutyl ammonium hydroxide), 0.080% leveling agent (Silwet™ L-7604),0.739% dye (Curcumin) and 83.920% ethyl lactate.

The resists were spun cast onto 41" YES oven HMDS primed silicon wafersand soft baked for 60 seconds at 140° C. (vacuum contact) on a GCAMicroTrac coat/bake track system. Coated wafers were then exposed with aGCA Excimer Stepper (fitted with a 0.53 NA lens) using a focus/exposurearray. Next, wafers were post exposure baked for 90 seconds at 140° C.(vacuum contact) and developed using a 25 second/25 second double-spraypuddle process on a GCA MicroTrac system using Shipley Megaposit CD-26developer (0.26N aqueous tetramethylene ammonium hydroxide developercontaining a leveling agent). Imaging conditions and resolution of thedeveloped relief images are set forth in Table 1 below for each of theResists A-D.

                  TABLE 1    ______________________________________                                   Masking                                          Focus  Ex-    Re-  Eo,   Esize,  %     Resolu-                                   Linearity,                                          Latitude,                                                 posure    sist mJ    mJ      UFTL  tion, μm                                   μm  μm  Latitude    ______________________________________    A    5.6   14.0    2.23  0.23  0.23   1.2    ±12.3%    B    9.0   21.0    2.07  0.24  0.24   1.0    ±10.5%    C    4.8   12.0    2.16  0.23  0.23   1.2    ±18.8%    D    5.4   13.0    3.20  0.24  0.24   1.0     ±7.9%    ______________________________________

EXAMPLE 6

In the following Example 6, the effect of use of a photospeed controlagent was further examined. Each of the photoresist compositions of thisexample (identified as Resists 1-5 below) contained a resin binder inthe same relative amount that was a copolymer of vinyl phenol andt-butylacrylate, having a M_(W) of about 20,000 and available under thetradename of Maruzen CTBA 161 from Maruzen Oil Company of Tokyo, Japan.The photoacid generator (PAG) used in the compositions of the exampleswas the sulfonate salt of Example 2 and formula I above. Ethyl lactatewas the solvent used in each of the compositions.

As specified in Table 2 below, the respective resist compositionscontained either no photospeed control agent (P.C.A. in Table 2), or aphotospeed control agent of tetrabutylammonium acetate (TBAOAc),tetrabutylammonium tosylate (TBAOTs), tetrabutylammonium triflate(TBAOTf) or tetrabutylammonium lactate (TBAL). The pK_(a) values of thephotospeed control agents used in each of resists 1-5 are also shown inTable 2.

The resist compositions were prepared by formulating ethyl lactatesolutions containing the resin binder, the PAG at 4% weight of the resinbinder, and the photospeed control agent (if present) at 9.6 μmol/g ofthe resin binder. All formulations were passed through Gelman Acro 0.2μm filters prior to use.

Separate wafers were coated with the resist compositions as described inExample 3 above and the coated wafers were exposed on a GCA XLS DUVstepper (KrF laser, NA=0.53, wavelength=248.4 nm) and postbaked at 140°C. for 90 seconds. The resists were developed with CD-26 using a 25/35 adouble spray puddle process.

The energy to clear (EO in Table 2) was defined as the exposure dosenecessary to remove the resist film upon development. Energy to size(Esize in Table 2) values were determined for 0.3 μM features asmeasured at the base of the resist image. Exposure and focus latitudevalues (EL and FL respectively in Table 2 below) were measured for 0.3μm features and were defined as the change in exposure dose or focusneeded to effect a ±10% change in linewidth. Linear resolution (Lin.Res. in Table 2) was defined as the size of the smallest feature within±10% of the nominal linewidth. Resolution (Res. in Table 2) was definedas the nominal linewidth of the smallest open feature.

Transmission IR spectra of the coated silicon wafers were obtained on aMattson Polaris FT-IR spectrometer using 64 scans at 4 cm⁻¹ resolution.IR contrast was defined as the change in magnitude of the 1150 cm⁻¹absorbance of the resin binder divided by the change in log exposuredose.

Chemical and lithographic data for each of the tested resists aresummarized in Table 2 below. In all cases, the presence of thephotospeed control agent results in improved resist performance.Moreover, the best results were obtained using the hydroxy-substitutedTBAL-containing resist, which has the best chemical contrast, exposurelatitude, focus latitude, and ultimate resolution. In addition, thatresist gave the smoothest, squarest profiles. The other resists showedconsiderably more roughness and irregularity, especially at the tops ofthe dense features.

                                      TABLE 2    __________________________________________________________________________    Resist      IR  EO  Esize           FL    Lin. Res.    No. P.C.A.             pK.sub.a                contrast                    mJ/cm.sup.2                        mJ/cm.sup.2                             Esize/EO                                  EL    μm μm Res. μm    __________________________________________________________________________    1   None -- -0.69                    1.0 dense: 1.8                             dense: 1.8                                  dense: 19%                                        dense: 0.79                                              dense: 0.30                                                    dense: 0.30                        iso: 1.9                             iso: 1.9                                  iso: 12%                                        iso: 0.75                                              iso: 0.25                                                    iso: 0.25    2   TBAOTf             -20                -0.74                    0.9 dense: 1.8                             dense: 2.0                                  dense: 18%                                        dense: 1.0                                              dense: 0.27                                                    dense: 0.27                        iso: 1.8                             iso: 2.0                                  iso: 14%                                        iso: 0.83                                              iso: 0.24                                                    iso: 0.24    3   TBAOTs             -7 -0.73                    0.9 dense: 1.9                             dense: 2.1                                  dense: 18%                                        dense: 0.91                                              dense: 0.27                                                    dense: 0.27                        iso: 1.9                             iso: 2.1                                  iso: 14%                                        iso: 0.94                                              iso:0.23                                                    iso: 0.19    4   TBAL 4  -1.0                    2.3 dense: 5.8                             dense: 2.5                                  dense: 22%                                        dense: 1.56                                              dense: 0.24                                                    dense: 0.23                        iso: 5.7                             iso: 2.5                                  iso: 14%                                        iso: 0.61                                              iso: 0.23                                                    iso: 0.22    5   TBAOAc             5  -0.83                    2.0 dense: 4.4                             dense: 2.2                                  dense: 21%                                        dense: 1.36                                              dense: 0.24                                                    dense: 0.24                        iso: 4.5                             iso: 2.3                                  iso: 18%                                        iso: 0.76                                              iso: 0.19                                                    iso: 0.18    __________________________________________________________________________

The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the spirit or scope of the invention asset forth in the following claims.

What is claimed is:
 1. A method for controlling photospeed of achemically amplified positive photoresist, comprising:(a) providing apositive photoresist composition comprising a resin binder with acidlabile groups, a photoacid generator, and a photospeed control agentthat is a lactate salt; (b) determining the photospeed of thephotoresist composition, and adjusting the photospeed to a desired valueby altering the amount of photospeed control agent in the composition.2. The method of claim 1 wherein an additional amount of the photospeedcontrol agent is added to the composition to adjust the photospeed. 3.The method of claim 1 wherein the photospeed control agent has a pK_(a)of about 10 or greater in non-salt form.
 4. A method for forming aphotoresist relief image comprising:applying a coating layer of thephotoresist composition onto a substrate the photoresist compositioncomprising1) a resin binder comprising acid labile groups, 2) aphotoacid generator that is a sulfonate compound, an onium salt, anitrobenzyl ester, an s-triazine or a halogenated non-ionic compound;and 3) a photospeed control agent that is a lactate salt imagewiseexposing to a source of activating energy; and developing to form arelief image.
 5. The method of claim 1 wherein the photospeed controlagent is a lactate salt of an organic amine.
 6. The method of claim 1wherein the photospeed control agent is a lactate salt of atetra-alkylammonium compound.
 7. The method of claim 1 wherein thephotoacid generator is a sulfonate salt.
 8. The method of claim 1wherein the photospeed control agent is a compound selected from thegroup consisting of: ##STR4##
 9. The method of claim 1 wherein thephotoacid generator is a sulfonate compound, an onium salt, anitrobenzyl ester, an s-triazine or a halogenated non-ionic compound.10. The method of claim 4 wherein the photospeed control agent is alactate salt of an organic amine.
 11. The method of claim 4 wherein thephotospeed control agent is a lactate salt of a tetra-alkylammoniumcompound.
 12. The method of claim 1 wherein the photospeed control agentis a lactate salt of a tetra-butylammonium hydroxide compound.
 13. Themethod of claim 1 wherein the substrate is a microelectronic wafer. 14.The method of claim 1 wherein the substrate is a flat panel displaysubstrate.
 15. The method of claim 4 wherein the photospeed controlagent is a lactate salt of a tetra-butylammonium hydroxide compound. 16.The method of claim 4 wherein the substrate is a microelectronic wafer.17. The method of claim 4 wherein the substrate is a flat panel displaysubstrate.
 18. A method for forming a photoresist relief imagecomprising:applying a coating layer of the photoresist composition ontoa substrate the photoresist composition comprisinga resin bindercomprising acid labile groups, a photoacid generator, and a lactate saltimagewise exposing to a source of activating energy; and developing toform a relief image.
 19. The method of claim 18 wherein the salt is alactate salt of an organic amine.
 20. The method of claim 18 wherein thesalt is a lactate salt of a tetraalkylammonium compound.
 21. The methodof claim 18 wherein the salt is a lactate salt of a tetra-butylammoniumhydroxide compound.
 22. The method of claim 18 wherein the substrate isa microelectronic wafer.
 23. The method of claim 18 wherein thesubstrate is a flat panel display substrate.